In recent years, various bone diseases, such as osteoporosis, fracture, and backache have increased on a global basis along with aging of society and the like, and have become a serious social problem. These diseases are caused by insufficient calcium intake, depression of calcium absorption ability, hormone imbalance after menopause, and the like. It is considered that increase the body bone mass as much as possible by activating the osteoblast and bone formation from the early stage of life, and increase the maximum bone mass and the bone strength (bone density+bone quality) is effective in preventing various bone diseases, such as osteoporosis, fracture, and backache. Note that the term “bone quality” refers to the bone microstructure, metabolic turnover, microfracture, and calcification. It is thought that various bone diseases, such as osteoporosis, fracture, and backache may be prevented by suppressing osteoclastic bone resorption. Bones are repeatedly resorbed and formed in a balanced manner (remodeling). However, various bone diseases, such as osteoporosis, fracture, and backache may occur when bone resorption exceeds bone formation due to a change in hormone balance after menopause, and the like. Therefore, bones can be strengthened by suppressing osteoclastic bone resorption and maintaining the bone strength at a constant level.
In view of the above situation, a drug, food, drink, feed, or the like, in which a calcium salt, such as calcium carbonate, calcium phosphate, or calcium lactate or a natural calcium product, such as whey calcium, bovine bone powder, or eggshell is added individually, has been administered in order to strengthen bones. A drug, food, drink, feed, or the like that contains such a calcium product together with a substance having a calcium absorption-promoting effect, such as casein phosphopeptide or oligosaccharide has also been used to strengthen bones. However, the calcium absorption rate is 50% or less when a food or drink that contains a calcium salt or a natural calcium product is administered, and the large part of the calcium administered may be discharged from the body without being absorbed. Moreover, even if calcium is absorbed into the body, it does not necessarily exhibit the bone metabolism-improving effect or a bone-strengthening effect, since the affinity to bones may differ according to its form or the type of nutritional ingredient administered together. An estrogen product, an active vitamin D3 product, a vitamin K2 product, a bisphosphonate product, a calcitonin product, and the like have been known as a drug for treating osteoporosis or strengthening bones, and new drugs such as an anti-RANKL antibody have been also developed. However, these drugs may have side effects such as buzzing in the ear, a headache, or loss of appetite. Moreover, the above substances are in a situation that they cannot be added to a food or drink at present from the viewpoint of safety, cost, and the like. Therefore, in light of the nature of various bone diseases, such as osteoporosis, fracture, and backache, development of such a bone-strengthening agent, food, drink, or feed that can be administered orally for a long time, increases the bone strength by promoting bone formation and suppressing bone resorption, and may be expected to have the effect of preventing or treating the various bone diseases has been desired.
There are several food materials that intends to improve the bone strength, for example, it has been reported that a basic protein derived from milk or a peptide fraction of an enzymatically degraded product thereof exhibits osteoblast proliferation activity, osteoclastic bone resorption suppression activity, and thus a bone-strengthening effect (see Patent Document 1). It has also been reported that angiogenin and lactoperoxidase, contained in a basic protein fraction derived from milk, independently have a function to improve the bone metabolism (see Patent Documents 2 to 4).